The present invention relates to a method and a system for controlling engine oil circulation, and more particularly, to a method and system for decreasing engine load in an initial operating period and properly controlling engine oil pressure such that pollutant emmisions are decreased.
The amount of pollutant emissions has become an important criterion for evaluating vehicle performance, and therefore it has become important to reduce pollutants in a vehicle. Pollutants exhausted from a vehicle include oxides of carbon such as carbon monoxide and carbon dioxide, as well as nitrogen oxides and hydrocarbons.
If fuel is incompletely burned, hydrocarbons are generated. Vehicles are now equipped with a catalytic converter, which is designed to reduce emissions from unacceptable to acceptable levels by re-burning the incompletely burned hydrocarbons. The catalytic converter only operates properly above a specific temperature (LOT: Lowest Operating Temperature), and because engine temperature is low in the initial operating period, there are many pollutant emissions at that time.
To reduce pollutant emissions in the initial operating period after startup, one may provide a lean air-fuel mixture or retard ignition timing. However, if the air-fuel mixture is lean or the ignition timing is retarded under high engine load conditions, the engine does not start or run properly. Therefore, reducing pollutant emissions in the initial operating period can be related to reducing engine load.
When the engine is operated, the engine drives many devices. An oil pump that provides lubricating oil to each part of the engine is one of the components driven by the engine, and therefore it increases engine load. In a conventional engine oil system, as shown in FIG. 1, the oil pump 13, driven by an engine crankshaft 12, generates oil pressure. The pressurized oil is provided into a main gallery through which it is provided to the engine. If the oil pressure is higher than a predetermined pressure, the oil pressure relief valve 15 is opened so that over-pressurized oil returns to an oil pan 11 via an oil return pipe 16. Therefore, the pressure of the oil pump is not maintained beyond the predetermined pressure. The oil pressure relief valve 15 is typically provided with a spring 17 and the predetermined pressure is determined by elastic power of the spring 17.
Thus, according to the present invention, a method and a system for controlling engine oil circulation, and decreasing pollutant emissions during an initial engine operating period are provided.
The system of the present invention thus may include a variety of sensors of engine performance parameters, a control unit receiving input from the sensors and plural valves controlled by the control unit to provide optimum oil circulation for increased engine performance and decreased pollutant emissions. More specifically, according to a preferred embodiment, an oil temperature sensor is disposed in a lower part of the oil pan to detect temperature of oil stored in the oil pan. An oil pressure sensor is disposed to detect oil pressure discharged from the oil pump. Also, an engine operation state sensor is provided to detect engine speed and engine load. Preferably an oil pressure relief valve and a solenoid valve are provided. The oil pressure relief valve is disposed in one side of the oil pump and bypasses oil to the oil pan when oil pressure supplied from the oil pump is higher than a predetermined pressure. The solenoid valve is disposed in the oil return pipe and controls oil bypass. As mentioned, a control unit preferably controls the operation of the solenoid valve based on data from the above sensors. The predetermined pressure of the oil pressure relief valve is set as a minimum pressure above which the engine works properly.
In a preferred embodiment, the control unit controls the solenoid valve on the basis of the oil temperature, the oil pressure and the engine operation state with a given control logic. The control logic prefereably includes a step of fully opening the solenoid valve if the starter motor operates until an engine speed is over a predetermined speed.
In a further aspect of the present invention an engine oil circulation control method is provided. According to a preferred enbodiment, the method includes opening an idle speed actuator (ISA) with a predetermined duty ratio if the ignition switch is turned on, opening the solenoid valve fully, and maintaining the solenoid valve to be fully open until the engine speed is higher than a predetermined speed. Furthermore, after the step of maintaining the solenoid valve to be fully open, the control method can further comprise a step of entering into an idle mode control where the solenoid valve is controlled on the basis of the oil temperature, the oil pressure and the engine operation state.
Preferably, the idle mode control comprises a number of control steps as follows:
The ISA is controlled by an air flow rate calculated by a given air flow rate function.
The solenoid valve is controlled by a duty ratio determined by a function of engine oil temperature, engine speed and engine load.
The air-fuel ratio is controlled by a given air-fuel ratio function such that the air-fuel ratio is high, but within a range where a fluctuation of engine speed can be regulated by ignition timing control.
The ignition timing is controlled by a given ignition timing function so as to eliminate fluctuation of engine speed in the case there is a fluctuation of engine speed. In addition to these control steps, a specific time (t(i)) is measured when the engine speed becomes higher than a predetermined idle speed.
Then, based on the gear-shift mode, the procedure is advanced to a xe2x80x9cDxe2x80x9d mode control step if a gear-shift mode is neither an xe2x80x9cNxe2x80x9d mode (neutral) nor a xe2x80x9cPxe2x80x9d mode (park), when the engine speed is higher than the predetermined idle speed.
If in either an xe2x80x9cNxe2x80x9d mode or a xe2x80x9cPxe2x80x9d mode, then it is determined whether an oxygen sensor temperature (To2) is lower than a predetermined Lambda feedback control temperature (TLOT), or a time elapsed after entering into an idle mode (t(i)-t(1)) is less than a predetermined time (ts(Tc)) determined by a function of a coolant temperature Tc, and then if the condition is not satisfied, the procedure is advanced to an ISA control step. Further steps include setting an ISA position as P1 in the case the oxygen sensor temperature (To2) is lower than the predetermined Lambda feed-back control temperature, and the time elapsed after entering into the idle mode (t(i)-t(1)) is less than the predetermined time (ts(Tc)) determined by a function of a coolant temperature, and determining whether a difference between a current and an immediate past engine speed is larger than a predetermined value, and if the difference is not larger than the predetermined value, advancing to the step of controlling the ignition timing, and otherwise advancing to the step of controlling the air-fuel ratio.